Fibrillar protein deposits are characteristic of the affected brain regions of Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, as well as many other neurodegenerative diseases. In addition, fibrillar deposits are characteristic of the abnormal pancreatic 13-cells in type II diabetes. The relationship between fibril formation and cell death is unclear, but convergent evidence suggests that fibrillization is causative. It is therefore critical to elucidate the molecular mechanism of fibril formation, so that therapeutic strategies can be devised to stop cell death. This grant is focused on the molecular description of the process whereby a normal soluble protein is converted, through a series of steps, into an insoluble, but ordered amyloid fibril. We have characterized a discrete transient intermediate in the process, designated a protofibril. This species may be the one responsible for disease pathogenesis. However, it is difficult to characterize due to its instability. We will bring to bear several different approaches, from chemical labeling and cross-linking to random mutagenesis, in order to discover a way to stabilize the protofibril intermediate and block its transition to the stable fibrillar state. It is our hope to generate tools, either small molecule inhibitors or inhibitory sequences, that can be used to test the pathogenicity of the protofibril in animal models and will also allow the protofibril to be stabilized and characterized. Finally, we will investigate one possible mechanism by which protofibrils could lead to cell death, that is, inappropriate and uncontrolled membrane permeabilization.